Animal replication-dependent histone mRNAs are the only eukaryotic mRNAs that lack a polyA tail ending instead in a conserved stemloop. In contrast mRNAs for histone variants, e.g. H3.3 and H2.v, are encoded by polyadenylated mRNAs. The genes for all five histone proteins are clustered in metazoan genomes, and factors required for histone gene expression are localized near the histone genes. We will determine the requirements for the coordinate expression of the replication-dependent histone mRNAs in vivo using Drosophila as a model system, and in particular the role of the Histone Locus Body in histone mRNA metabolism. We will use both biochemical and genetic approaches to determine 1. The structural requirements in the HLB components FLASH and NPAT required for efficient production of properly processed histone mRNA, 2. The sequences in the histone gene locus that specifies the formation of the HLB at the histone locus and 3. The composition of the histone cleavage factor, which contains polyadenylation factors Symplekin, CPSF73 and CPSF100, will be determined and the role of Symplekin in histone pre-mRNA processing in vitro and in vivo elucidated.